Purification of gas with soil microorganisms



Nov. 9, 1965 J. N. BAPTIST 3,216,905

PURIFICATION OF GAS WITH SOIL MECROORGANISMS Filed June 12, 1963INVENTOR JAMES N. BAPTIST AGENT United States Patent 3,216,905PURIFICATION OF GAS WITH SOIL MICROORGANISMS James N. Baptist,Clarksville, Md., assignor to W. R. Grace & Co., New York, N.Y., acorporation of Connecticut Filed June 12, 1963, Ser. No. 287,344 2Claims. (Cl. 195-2) The present invention relates to the purification ofair, and more specifically to a novel method which may be used to removeobnoxious and undesirable impurities from air.

The prior art shows numerous devices for removing impurities from air.For example, devices containing activated charcoal and other absorbersare frequently used to absorb odors and dangerous gaseous impuritiesfrom an air stream. Other devices utilize a principle wherein odorousconstituents of a gas stream are oxidized and hence converted toinnocuous carbon dioxide. The so called ozone purifier is an example ofsuch a device.

These prior art devices possess inherent drawbacks in that they eitherbecome rapidly saturated with organic odor producing materials orrequire the consumption of considerable electrical energy and in somecases impart dubious benefits. An air purification system which is trulyself regenerating and self energized would indeed represent a usefuldevelopment in the art of air purification and odor removal. Such adevice would find wide application in confined areas having limitedstorage and power facilities such as fall out shelters and submarines,as well as in accessible areas of habitations such as animal houses andhomes.

It is therefore an object of the present invention to provide animproved method for removing impurities from air.

It is another object to provide a self regenerating energized system forremoving obnoxious and harmful substances from an air stream.

It is a further object to provide a self contained device which willcontinuously oxidize objectionable organic odor causing materials in airwith a minimum of expense and maintenance.

These and still further objects of the present invention will becomereadily apparent to one skilled in the art from the following examplesand drawings wherein:

FIG. 1 is a cross-sectional view of a bacteria supporting cell which maybe used in the present invention; and

FIG. 2 is a cross-sectional view of air purification system whichutilize the teachings of this invention.

Broadly, the present invention contemplates the method for removingobjectionable components from an air stream which involves passing animpurity laden air stream through a porous supporting medium whichcontains microorganisms capable of oxidizing objectionable organiccompounds.

, More specifically, I have found that if an ordinary soil microorganismculture is placed on a supporting medium which contains only water andnecessary nutrient inorganic salts, and an air containing obnoxiousorganic component is passed therethorugh, the microbes will etfectivelyand completely oxidize the odorless organic materials to innocuouscarbon dioxide. The microbes will live indefinitely on the odor causingorganic material in the air stream, and no external power need beapplied to the system other than that used to maintain a current of airthrough the system. Furthermore, present system which ice utilizesmicrobial cultures never requires regeneration or replacement so long asthe medium is kept moist and in contact with odor laden air.

A more thorough understanding of the present system may be obtained fromreference in FIG. 1 which illustrates a cross-sectional view of amicroorganism support generally 10 which is used in the practice of theinvention. It is seen the support 10 comprises a support housing 11which generally consists of an elongated container provided with amultiplicity of holes 12 through which odor laden air may pass. Thefaces of support housing 11 may be made of an expanded mesh screen orother material having suflicient porosity to permit a large stream ofgas to pass through. The holes 12 must be sufliciently small to maintainsupport material 13 therein.

Support material 13 shown in FIG. 1 comprises a quantity of finelydivided material such as expanded mica, foamed plastic, vermiculite,sand, glass wool, or any other suitable finely divided material having alarge surface area. This material is admixed with the inorganic saltsand water necessary to support microorganism growth. The microbes (notshown in the drawing) are distributed throughout the support material13. At the bottom of the support housing 11 in FIG. 1, is a tray-shapedreservoir 14 which maintains a supply of mineral solution generallyindicated as 15. This solution is maintained at the bottom of thesupport material and in contact therewith. The water 15 by capillaryaction is distributed throughout the support material to provide asuitable condition for microorganism growth. Alternatively, the nutrientmineral solution may be sprayed continuously over the support material.

FIG. 2 illustrates an embodiment of the present invention wherein themicroorganism support structure 10 has been incorporated in a forced airdistribution system.

In FIG. 2 it is seen that the microbe support system structure 10 (asportrayed in FIG. 1) is placed within a duct 20 down stream from a fanor blower system 21. Down stream from the microbe structure 10 islocated an air treating device generally 25 which may be adapted toeither heat or cool the air which subsequently passes through microbesupport structure 10. Air treating structure 25 may be adapted forheating or cooling by passing either a hot or cool fluid through coils26. Air treating system 25 is provided With fluid inlet 28 and fiuidoutlet 27.

In the event air treating system 25 is adapted for cooling, whichnecessarily results in some condensing of the water from the air streamwhich passes through the moist bacteria support material, condensatecollector 30 in the form of a tray placed beneath the treating device25, which is equipped with condensate of drain 31, provides means forcarrying away condensed water.

In operation, it is seen that forced air from blower 21 is forced downduct 20 in the direction illustrated by arrow 35. The air is then forcedthrough microbe support structure 10 including the microbe supportmaterial 13 as illustrated by arrow 36. In coming in contact with thesupport material the organic constituents of the air are thoroughly andcompletely oxidized to carbon dioxide by microorganisms containedtherein. The odor free air then passes through the air treating device25 which either cools or heats as desired. Finally the purified andtreated air stream passes from the device as illustrated by arrow 37.The air subsequently may be conducted to a ventilated space.

The microbe support material used in the practice of the presentinvention may be any particulate material which is capable ofmaintaining sufiicient moisture and nutrient salts required to supportmicrobe growth. The material should also provide sufiicient surface areato air passing therethrough for contact with microbes with sufficientthoroughness to provide complete oxidation. Typical materials areexpanded vermiculite, sand, glass wool or a synthetic plastic material(foamed polystyrene, polypropylene fibers, etc.).

The microorganism cultures used to catalyze the oxidation reactions ofthe present invention are preferably natural mixed populations of soilmicroorganisms. It is possible to use a pure culture of a singlebacterium or fungus. However, such cultures are difficult to protectfrom contamination. In addition, the process is not trulyself-regenerating if a pure culture is used because the mineral elementsgradually become tied up in a nonavailable form. With mixed cultures, abalanced population develops which depends on organic materials in theair stream for its energy source. Then protozoans and nematodes consumethe bodies of other organisms and return the mineral elements to anavailable form. The net result is that the population as a whole acts asa catalyst for oxidation of organic materials in the air stream to COUnder steady state conditions, no important overall change occurs in themicrobial population and thus the population as a whole may beconsidered an oxidation catalyst.

As indicated above, in order to provide a growing and vigorous microbialculture there must be an ample supply of water. This means that thesupport material should be substantially saturated with water while thesystem is in operation. The water should also be provided with suitableinorganic nutrient materials necessary for sustained growth. Theserequired inorganic nutrients include suitable amounts of NHJ, K+, NaMg+, Ca+, Fe+++, SO 7, HPO4 H PO Cl, Co++, Mn++, Zn++, and Cu++ whichmay be impregnated into the support material in the form of a solution,and then dried. Subsequent addition of water to the support materialwill provide the required growth medium.

In a slightly modified embodiment of those described above, asubstantially dry absorbing support material such as activated charcoalmay be used. This material may be saturated with microorganisms andnutrient mineral solution, then dried and placed in support 10. The dryactivated charcoal will then physically adsorb the offensive organicmaterials from a substantially dry gas stream in a conventional manner.After the charcoal support material has been saturated with offensiveorganic matter, water may be added, and the biological degradation willoccur as set forth previously. The advantage obtained from such amodification resides in the fact a substantially dry condition may bemaintained in the system. This permits the direct production of dry odorfree air without subsequent water removal.

When the aforedescribed dry unit is used in conjunction with the systemset forth in FIGURE 2, it is generally preferred that two or morealternatively acting parallel connected units be used. This permits onedry unit to be in filtering operation while the other unit is moistenedand regenerated by biological means.

The temperatures required for adequate operation of the present devicegenerally range from about C. to about 60 C., but best operation occursat -30 C. Ordinarily these temperatures are provided in the normalhabitable space required having air required to be treated in accordancewith the present invention.

The illustrated embodiment of FIGURE 2 may be conveniently incorporatedin the normal forced air heating system present in a home. Furthermore,special devices mounted in consoles or other suitable housings may beplaced in a room or a space which requires air purification. Themicrobes will oxidize practically any organic material coming in contacttherewith, providing the population has time to become adapted to thematerial. The present devices may be used to remove certain toxic gasessuch as nerve gases and other dangerous materials which may be used inbiological warfare.

For example, if a nerve gas is to be removed, an enrichment culturetechnique is used to obtain a microbial population able to oxidize thegas. Then this mixed population is added to the microbial support.

To graphically illustrate the effectiveness of the present invention thefollowing example is given which was conducted on a laboratory scale.

Example I A column of about 2 feet long and 3 inches in diameter waspacked with sand then saturated with a growth medium made as follows:

G. (NH SO 10.0 KH PO 10.0 Na I-IPO -7H O 18.9 MgSO 2.0 CaCl 0.20 FeCl0.10 H 0, 1 liter.

Co Mn++, Cu' and Zn++ were added in trace quantities. A few grams ofsoil were added to the col umn as an initial source of microorganisms.The odor source for this experiment was obtained by mixing CaCO withcheese and inoculating the mixture with soil. After CaCO neutralized thecheese acids, protein decomposing bacteria, clostridia, grew underanaerobic conditions and produced the very well-known odor of fermentingproteins. This odor source was constructed first and incubated 4 daysuntil a strong odor was produced. The compounds causing this odor wereundoubtedly ptomaines and related compounds. Then, this odor was mixedwith a moist air stream and passed through the deodorizer describedabove. At first, the odor came through the device. However, afterseveral days, it had become noticeably weaker, and after 7 days, theodor of ptomaines was nearly gone. This device was operated successfullyfor an additional 5 weeks. It was still removing the odor when it wasdisassembled. Since odor detection is somewhat subjective, 7 Witnesseswere asked to examine the device during the period of its operation. Allwere very positive that the odor was removed.

Example II The fact that odor came through the device of Example I forthe first few days is proof that odor removal was due to microorganismsrather than physical adsorption to soil or sand particles. To check thispoint again, a second device was made exactly like that in Example I.Then it was sterilized by steam heat at C. for 1 hour. When this devicewas connected to the odor containing air stream, a very strong ptomaineodor came through within 2 hours.

The above clearly illustrates that highly eflicient and practicalodor-removing devices may be produced in accordance with the presentinvention. The use of a mixed microbial population provides a systemwhich requires no periodic regeneration and no outside power source.

I claim:

1. A method for removing obnoxious organic materials from gases whichcomprises passing a substantially dry gas stream containing obnoxiousorganic impurities. in contact with a substantially dry adsorbentmaterial capable of physically adsorbing said impurities from said airstream, said adsorbent material being impregnated with a mixture ofviable soil microorganisms in a dormant state and nutrient salts,removing said adsorbent material from said air stream when said materialis substantially saturated with organic impurities, and adding Water tosaid saturated adsorbent material, to activate said soil microorganismsand oxidize said impurities.

2. The method of claim 1 wherein said adsorbent material is activatedcharcoal.

References Cited by the Examiner UNITED STATES PATENTS REUBEN FRIEDMAN,Primary Examiner.

1. A METHOD FOR REMOVING OBNOXIOUS ORGANIC MATERIALS FROMGASES WHICHCOMPRISES PASSING A SUBSTANTIALLY DRY GAS STREAM CONTAINING OBNOXIOUSORGANIC IMPURITIES IN CONTACT WITH A SUBSTANTIALLY DRY ABSORBENTMATERIAL CAPABLE OF PHYSICALLY ABSORBIN SAID IMPURITIES FROM SAID AIRSTREAM, SAID ADSORBENT MATERIAL BEING IMPREGNATED WITH A MIXTURE OFVIABLE SOIL MICROORGANISMS INA DORMANT STATE AND NUTRIENT SALTS, RMOVINGSAID ABSORBENT MATERIAL FROM SAID AIR STREAM WHEN SAID MATERIAL ISSUBSTANTIALLY SATURATED WITH ORGANIC IMPURITIES, AND ADDING WATER TOSAID SATURATED ABSORBENT MATERIAL, TO ACTIVATE SAID SOIL MICROORGANISMSAND OXIDIZE SAID IMPURITEIS.